/**
 * Created by zhourh on 2018/5/24.
 * 给定两个二叉树，想象当你将它们中的一个覆盖到另一个上时，两个二叉树的一些节点便会重叠。

 你需要将他们合并为一个新的二叉树。合并的规则是如果两个节点重叠，那么将他们的值相加作为节点合并后的新值，否则不为 NULL 的节点将直接作为新二叉树的节点。

 示例 1:

 输入:
 Tree 1                     Tree 2
 1                         2
 / \                       / \
 3   2                     1   3
 /                           \   \
 5                             4   7
 输出:
 合并后的树:
 3
 / \
 4   5
 / \   \
 5   4   7
 注意: 合并必须从两个树的根节点开始。

 考察得是递归的使用

 */
public class MergeTwoBinaryTrees {

    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        t1.left = new TreeNode(3);
        t1.right = new TreeNode(2);
        t1.left.left = new TreeNode(5);

        TreeNode t2 = new TreeNode(2);
        t2.left = new TreeNode(1);
        t2.right = new TreeNode(3);
        t2.left.right = new TreeNode(4);
        t2.right.right = new TreeNode(7);

        printTree(new MergeTwoBinaryTrees().mergeTrees(t1, t2));
    }

    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        if (t1 == null && t2 == null) {
            return null;
        } else if (t1 == null) {
            return t2;
        } else if (t2 == null) {
            return t1;
        }

        TreeNode resultTreeRootNode = new TreeNode(t1.val + t2.val);
        resultTreeRootNode.left = mergeTrees(t1.left, t2.left);
        resultTreeRootNode.right = mergeTrees(t1.right, t2.right);

        return resultTreeRootNode;
    }

    public static void printTree(TreeNode t) {
        if (t != null) {
            System.out.print(t.val + ", ");
            printTree(t.left);
            printTree(t.right);
        }
    }
}
